A rotary type straightener may be used to straighten a cold-drawn annealed tube and consists of rolls set with axes oblique with the pass line. These rolls are somewhat smaller in the center than at the ends to afford a line contact with the tube, which passes between the two driven rolls on one side and the three idle rolls on the other. The tube is helically advanced by the rolls which are adjusted to bend the tube progressively as it moves through the machine. Since the tube to be straightened is advanced by the oblique rolls, the tube must preclude any extension transversely formed on the tube. Therefore, a bolt with screw head can not be straightened by such a conventional rotary type straightener.
The present invention has found the drawback of a conventional rotary type straightener and invented the present wheel-driving straightener, especially suitable for straightening a screw bolt.